The present invention relates to a rigid endoscope of oblique window type having improved distribution characteristics of illuminating light.
There have been employed endoscopes for the observation and diagnosis of an object such as organ or the like in a body cavity by inserting the elongated probe into the body cavity or the like for focusing the object by means of objective optical system formed at the tip of the probe.
Such endoscopes include flexible endoscope wherein the probe is flexible and adapted to observe the object in the body cavity through the oral cavity or the like and nonlinear passage and rigid endoscope wherein the probe is rigid and inserted substantially linearly.
Although such a rigid endoscope cannot be inserted easily through a flexible passage, it has an advantage that it provides more distinct image by employing image transferring means such as relay lens system or the like over those obtained by employing a flexible image guide fibre bundle. Because of the rigid structure, it is incompatible with the body cavity to limit the observable field so that the endoscope having visual direction such as straight window type or oblique window type should be chosen depending on the object to be observed.
As seen from a conventional embodiment as shown in Published Japanese Patent Application No. 190913/1983, an endoscope of oblique window type realizes desired light distribution characteristics so as to enable illumination over any desired range of view by bending the tip of the light guide inserted through the inserting probe, by means of a leading tip member, or the like, for transmitting and radiating the illuminating light or bending the tip of the pipe inserting light guide, or the like, therethrough and radiating the light through the output window of the light guide inserted through said bend portion, thereby illuminating the portion observable by the objective optical system in the oblique direction.
However, in such means, the outer diameter of the probe is relatively large and the tip member requires a space for receiving or attaching the tip member and has a large diameter. When the illuminating light is radiated to the desired direction by bending the tip member without damaging it, the means function efficiently. However, when a rigid endoscope having a fine diameter probe is employed, there is provided no space for attaching the tip member as set forth above or no sufficient bend when the tip member is inserted through a bended pipe. Thus, light distribution characteristics to the desired direction is not provided.
As prior art for radiating the illuminating light by deflecting to a desired direction, there has been known light deflecting means as shown in U.S. Pat. No. 3,278,738. According to this patent, the means are provided with a fibre bundle comprising an illuminating optical system around the objective optical system of microscope. The tip of the bundle is tilted to the outer periphery side with respect to the radial direction, thereby deflectioning the illuminating light guided through the fibre bundle so as to concentrate the light to the object to be observed through the inclined window at the tip of bundle. This increases the intensity of illumination to the object to be observed for observing the object directly and effectively through the objective lens arranged at the tip of the objective optical system.
However, when light deflection means are applied to an endoscope of oblique window type, the objective lens should be arranged at the tip of the objective optical system so as to be tilted at a predetermined angle with respect to the central axis of said objective optical system, and with respect to the visual range to radiate the illuminating light to the visual direction. Hence, when such a structure is applied to an endoscope of oblique window type, it is impossible to radiate the illuminating light to the direction of object with the required intensity.